Maybe I was a bit vague in the fault tolerance statement. What I mean is to have a high availability in your services, e.g: using AWS ASG for your servers, having more than one replica for your Kubernetes pods.

If one of the servers/pods fail, the process behind detects them as "unhealthy" (having a nice monitoring/alarming as you mentioned) and replaces them with a new server with the same software characteristics so, for the end-user, SO, your client. Nothing has changed, the load just moved to a single instance for about 5-10 mins until a new server was deployed.